Many minimally invasive or noninvasive interventional medical devices and procedures have been used to treat defects in the vasculature which are not easily reached by surgical procedures. Such medical devices which are adapted for implantation in body lumens in order to support weakened or occluded vessel walls and allow fluid flow are well known and commercially available. One such device is a vascular stent, for example. Stents may be employed to prop up vessel walls and maintain openings in vessels in the coronary system, the brain, the urinary, biliary, esophageal, tracheal and bronchial tracts, and so forth.
However, in some situations, it is desirable to block fluid flow. For example, one serious defect in the vascular system is an aneurysm which is an area of a weakened vessel wall that causes a bulge or bubble to protrude from the adjacent vessel. If untreated, an aneurysm may continue expanding until it bursts, causing hemorrhage. It is therefore often desirable to block fluid flow to the aneurysm.
Devices used for the treatment of such defects may be referred to as vaso-occlusive devices and are commonly deployed to the aneurysm site through the use of a catheter device. Vaso-occlusive devices can have a variety of configurations, and are generally formed of one or more elements that have a deployed configuration for blocking blood flow which is different from their configuration during delivery to the site.
Probably the most widely used method of treating aneurysms endovascularly is coil embolization. However, while this method is very effective for aneurysms having a smaller neck size, it is not as easily used for wide-necked or giant aneurysms because it is more difficult to fill the aneurysm sac adequately and/or to maintain the stability of the coils inside the sac.
Devices for bridging the necks of wide-necked or narrow-necked aneurysms are found, for example, in U.S. Pat. Nos. 5,935,148, 6,063,070, 6,036,720, 6,063,104 and U.S. Pat. No. 6,139,564. These devices may also be used to stabilize the placement of vaso-occlusive devices such as helically wound coils, i.e. coil embolization methods, in the aneurysm or may be used to, at least partially, close the aneurysm neck. The aneurysm neck bridge or retainer assemblies described in the patents above may be delivered to the aneurysm in a variety of different ways, but preferably are attached to an electrolytically severable joint for their deployment. After deployment of the neck bridge or retainer, the aneurysm is at least partially filled with a vaso-occlusive device such as a helically wound coil. The vaso-occlusive devices may also be delivered to the aneurysm using a number of different methods such as by a core wire which is linked to the coils by an electrolytically severable joint or a mechanically severable joint. The vaso-occlusive devices may also be simply pushed into the aneurysm. The success of such devices as those described above may depend on several factors, however, including whether or not the device can migrate out of the aneurysm through the neck of the aneurysm.
Another example of a vaso-occlusive device applicable to the treatment of an aneurysm is a covered stent or a stent-graft. Some covered stents have a limited usefulness due to the stiffness of the device, and synthetic grafts themselves have a tendency to occlude when employed in small blood vessels. Arteries where there is an aneurysm typically have a lot of branching, and when employing a covered stent, there is a further risk of occluding the small branch vessels arising from the parent artery rather than simply blocking the neck of the aneurysm as desired.
Thus, it would be beneficial to have a vaso-occlusive device that can be delivered to an aneurysm or other body vessel in a primary unexpanded configuration, wherein such device can be deployed and released to assume a secondary, expanded configuration which occludes the neck of the aneurysm, and which can be anchored at the site of the aneurysm so that it does not migrate from the site.